MusicKit output parity

[bolsinga]

Goal is to use newer MusicKit over iTunesLibrary. However there are some issues with MusicKit blocking this effort.

• No sorted Artist nor Album names: FB15554956
• No Song.discNumber set: FB15563446
• Nothing equivalent to ITLibMediaItem.year (not even Song.releaseDate): FB15563462

This will be updated if more issues are found.

[bolsinga]

Also no modified Date: FB15762879